Expected Damage From Displacement of Slow Moving Slides
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Transcript of Expected Damage From Displacement of Slow Moving Slides
Landslides (2011) 8:117–131DOI 10.1007/s10346-010-0227-7Received: 27 March 2009Accepted: 12 May 2010Published online: 16 June 2010© Springer-Verlag 2010
Mohamed Farouk Mansour I Norbert R. Morgenstern I C. Derek Martin
Expected damage from displacement of slow-movingslides
Abstract Facilities such as buildings, highways, railways, bridges,dams and pipelines often are built on natural slopes where the riskof landslides is not low. The vulnerability of these facilities to slow-moving slides has sometimes been underestimated, although thevelocity of some classes of slow slides is uncontrollable. More than50 cases of slow slides were compiled from the literature for thisstudy. Some statistics about the movement trigger(s), the methodsused to measure displacement, the material forming the rupturesurface and the type of the vulnerable facilities are presented. It isshown that the expected degree of damage to urban settlements,highways, bridges and dams can be related to the slide velocity oraccumulating displacement. Buildings and residential houses maytolerate higher slide velocities and total displacements than otherfacilities before experiencing serious damage. Movements as low as100mmmay severely damage bridges, but such low rates may causeonly moderate damage to urban communities. The relationshipbetween movement and the expected extent of damage should beuseful to geotechnical engineers who deal with different classes ofslow slides and will help in the choice of appropriate mitigationmeasures based on preliminary estimates of movement rates.
Keywords Slow-moving slides . landslide-induced damage .
damage description . landslide velocity . vulnerability to slides
IntroductionVulnerability is the degree of loss for a given element at riskresulting from the occurrence of a natural phenomenon such as alandslide. It is usually expressed as a value ranging from zero toone. Vulnerability is one of two factors used to evaluate the specificrisk. The other element is the natural hazard. Natural hazard isdefined as the probability of occurrence of a potentially damagingphenomenon, such as a landslide, within a certain period of timeand a specific area. Specific risk is mathematically expressed as theproduct of the hazard and the vulnerability (Varnes 1984).
The vulnerability to a landslide can be assessed by comparingthe value of the resulting damage to the actual value of thevulnerable facility (Remondo et al. 2004). The steadily increasingpopulation throughout the world has led to a considerable rise inurban development in landslide-prone areas. Urban landslides aretriggered mainly by seasonal hydrological, environmental andanthropogenic changes, such as rainfall, earthquakes and humanactivities. The adverse effects of urban landsliding have been mademore severe by uncontrolled population growth in hillside areas insome countries. Therefore, the risks arising from urban develop-ment in landslide-prone areas are increasing despite the progressin the application of mitigation measures.
Landslide movement types fall into five main categories: fall,topple, spread, flow and slide. While this paper focuses on slides, thefive main categories will be defined briefly to illustrate the generaldifferences between them. A fall occurs when the shear resistancealong a surface inside a steep slope becomes very low or zero, so soilor rock descends through the air by falling. The velocity of this kind
of landslides is very rapid to extremely rapid. Falls may occur as freefall, bouncing or rolling. A topple is the rotation of a soil or rockmass around an axis that lies below the center of gravity of thedisplaced material. Toppling could occur due to the weight ofmaterials upslope of the displaced soil or rock, or due to waterbuilding up in cracks in the soil or rock mass. Topples can beextremely slow or extremely rapid. Spread is the extension, andhence fracturing, of a cohesive soil, accompanied by subsidence overan underlying softer material. Flows are rapid movements in whichthe shear surfaces are closely spaced and not preserved. Thedistribution of velocity within the moving mass is similar to that ofa viscous liquid. The basal detachment surface of a flow is thick. Aslide, in contrast, is the downslope movement of soil or rock onrupture surfaces that are relatively thinner than those of flows andwhere intense shear strain has taken place (Cruden and Varnes 1996).
While the losses resulting from rapid landslides such as debrisflows, mud flows and rock falls are the highest and most severe,slow-moving slides also have adverse effects on affected facilities.The accumulation of slow movement can lead in some cases to totaldisruption of the serviceability of these facilities. Loss of life mayresult as well. Slow slides fall into three classes (Cruden and Varnes1996):
– Extremely slowly moving slides: this class includes slidesmoving at rates ranging from 0 to 16 mm/year.
– Very slow-moving slides: this class includes slides moving atrates ranging from 16 mm/year to 1.6 m/year.
– Slow-moving slides: this class includes slides moving at ratesranging from 1.6 to 160 m/year (∼13.3 m/month).
This study used the available literature to describe the damageto different facilities caused by the different classes of slow slides.The vulnerable infrastructure includes urban and suburbansettlements, highways and railways, bridges, dams and lifelinessuch as pipelines. The main information required from each of thereviewed cases is the movement rate and the extent of damagecaused. The different attributes of the reviewed cases, such as themethod used to measure the movement, the type of materialscontrolling the movement and the likely trigger(s) of movement,were highlighted, and some elementary statistics were calculated.
The analysis allows the typical (or expected) extent ofdamage to be related to the rate (or more usually the amount)of movement. Separate analyses are made for each class of thesurveyed infrastructure. The damage extent is not vulner-ability, but case histories rarely document the original value ofthe vulnerable facility and the cost of repairing the damage.The extent of damage resulting from slides of a certain velocityis the most common information mentioned in the cases cited.
Characteristics of slow-moving slidesMore than 50 cases of slow-moving slides were reviewed in thestudy. The cases cover instabilities in many countries in the world:
Landslides 8 & (2011) 117
Technical Note
Table1Summaryof
thereviewed
cases
Case
number
Reference
Materialhostingthe
rupturesurface
Displacement
measurementmethod
Movem
entrate
(mm/year)
Durationof
monitoring
Trigger
Vulnerablefacility
1Lim
itedandEdmonton
(1992)
Preglacialclays
andclay
shale
Inclinometers
143months(one
SIwas
installedfor7
years)
–TownofPeaceRiver,Alberta,
Canada
2Clifton
etal.(1986)
Clay
shale
Inclinometers
108
1–1.5years
Rivererosion
Regina
beachin
Saskatchew
an,Canada
3Clem
entinoet
al.
(2008)
Presheared
bentonitic
clayshaleand
sandstone
Inclinometers
35During2001
Water
pondingon
the
slope
Highway
eastof
thetownof
DraytoninAlberta,Canada
4Hayley(1968)
Clay
shale
Inclinometersandsurface
monum
ents
100
5months
Rivererosion
Highway
49andtheLittle
Smokybridge
inAlberta,
Canada
5BrookerandPeck
(1993)
Clay
shale
Personalestim
ates
90–120
2years
Toeerosion,precipitation
andhorizontalforces
from
thebridge
anchor
PeaceRiversuspension
Bridge
andawater
pipeline,British
Columbia,
Canada
6Moore
etal.(2006)
Clay
Inclinometersandsurface
monum
ents
10–14
Recent
monitoring
lasted
4years
Reservoirlevel
fluctuations
and
rainfall
Mica
Dam,British
Columbia,
Canada
7BrookerandPeck
(1993)
Clay
shale
Inclinometers
100
5years
Rainfall
Oilw
ellcasing,Sw
anHills,
Alberta,Canada
8Barlow(2000)
Clay
shale
Geom
orphologicevidence
188
Notindicated
Stream
incision
Pipeline,FortMcM
urray,
Canada
9Esser(2000)
Plastic
lacustrineclay
Inclinometer
306
5years
Constructionactivities
Residentialcom
plex
inOhio,
USA
10BrookerandPeck
(1993)
Clay
shale
–100
13years
Bridge
construction
TheBism
arck
Bridge
across
theMissouriRiver,USA
11Bressaniet
al.(2008)
Interface
between
overlying
colluviu
mandclayeysiltstone
Inclinometers
34(upto
80)
22months
Rainfall
Urbanslope
inSantaCruz
doSul,Brazil
12Ibadango
etal.(2005)
Sedimentaryrocks
DifferentialG
PS6,000
2months
Constructionactivities
Urbansettlem
entson
the
elongatedvalleyof
the
Lojabasin
inEcuador
13Jworchan
etal.(2008)
Colluviu
mandinterface
betweenresidualsoils
andbedrock
Inclinometers
125months
Rainfall
Aslope
proposed
for
residentialdevelopmentin
theWestPennantHills,
Sydney,A
ustralia
14GillonandSaul(1996)
Sandysiltclaygouge
Aerialsurveydata
180
42years
Rainfall
ClydeDam,N
ewZealand
15Cascinietal.(2008b)
Quaternarydeposits
DifferentialSynthetic
Aperture
Radar
Interferometry(D-InSAR)
55years
Rainfall
A489km
2nextto
Liri-
Garigliano
andVolturno
RiversinItaly(urban
developm
ent)
16Wasow
skietal.(2008)
Clay
PersistentScatterers
Interferometry
84years
Rainfallandconstruction
activity
Casalnuovo
Monterotaro
and
Pietramontecorvinotowns
inItaly
Technical Note
Landslides 8 & (2011)118
Table1
(continued)
Case
number
Reference
Materialhostingthe
rupturesurface
Displacement
measurementmethod
Movem
entrate
(mm/year)
Durationof
monitoring
Trigger
Vulnerablefacility
17Calcaterra
etal.(2008)
Rock
PermanentScatterers
Synthetic
ApertureRadar
Interferometry(PS-
InSAR)
and
inclinometers
169years
Rainfall
Buildings
oftheMoiodella
Civitellavillage
inSalerno,
Italy
18Buccoliniand
Sciarra
(1996)
Marlyclays
Inclinometersandsurface
monum
ents
19–26
15months
Rainfall
Dwellinghouses
anda
highway
intheAbruzzo
region,Italy
19Spizzichinoet
al.
(2004)
Clay
Airphotos
4,000
25years
Rainfallandhuman
activity
Cragovillage
inItaly
20Cascinietal.(2008a)
Softenedclay
Inclinometers
442.5years
Rainfall
Amajor
road
andtheRome-
Florencerailw
ay
21Ceccucciet
al.(2008)
Quaternarydepositsand
dislocatedbedrock
Inclinometers
659years
Rainfall
Collapseof
along
stretchof
anationalroad,theSerre
LaVoutelandslide,N
orth
WestItaly
22D’Eliaet
al.(2000)
Interface
betweenweak
andcompetent
rock
Inclinometers
132
3months
Rainfall
TheIoniccoast,Italy
23Catalano
etal.(2000)
Clay
Inclinometers
127
11years
Reservoirfilling
Trinita
Dam,Italy
24Catalano
etal.(2000)
Softenedclaylayer
Topographicmonum
ents
110
Inferredto
be1year
Reservoirfilling
CasanuovaDam,Italy
25BartonandMcCosker
(2000)
Rock
Inclinometers
1216
years
Rainfall
CoastalcliffinAftonDown,
UK
26Fortet
al.(2000b)
–Inclinometersandsurface
surveying
911year
Coastalerosionand
rainfall
Seaw
allstructures,roads
and
footpathsinthetownof
LymeRegis,UK
27Fortet
al.(2000a)
Stiff,fissured
overconsolidated
Bartonclay
Surface
surveying
861
3.5years
Toeerosionandrainfall
Buildings
ontopof
acliffat
Barton-on-Sea
shorein
Hampshire,U
K
28BeaumontandForth
(1996)
Glacialdeposits
ofsands
andgravelsoverlying
boulderclay
Inclinometers
13.8
4months
Miningactivities
Wideningof
arailw
ayem
bankmentinthe
countyof
Durham
,UK,in
orderto
constructanew
duallane
carriagew
ay
29LeeandClark(2000)
Glacialtill
Surface
surveying
560
2and4years(both
periods
confirm
edthesamerate)
Rainfallanderosion
Coastalcliffinstabilitiesalong
theScarboroughCoast,UK
affected
aroad
30NicholandLowman
(2000)
Interface
betweentill
andmudstones
and
siltstones
–600–6,000
Inferredby
authorsto
be1month
Rainfall
TheA5
Trunkroad
between
London
andDublin,U
K
31Carson
andFisher
(1991)
Bentoniticlayers
–23
13years
Riverdowncutting
Anancientbridge
inthecounty
ofShropshire,England
32Bonnardet
al.(2008)
Clay
shale
Surface
surveying
techniques
10Notindicated
–TriesenandTriesenberg
villagesineastern
Switzerland
33Bonnardet
al.(2000)
–Surface
surveyingand
inclinometers
6032
yearsforsurface
surveying
Rainfall
Polmengo
bridge
nearFaido,
Switzerland
Landslides 8 & (2011) 119
Table1
(continued)
Case
number
Reference
Materialhostingthe
rupturesurface
Displacement
measurementmethod
Movem
entrate
(mm/year)
Durationof
monitoring
Trigger
Vulnerablefacility
34Blikra(2008)
Rock
Extensom
eters,GPS,total
stationand
inclinometers
30–100
(upto
365)
Ranged
frommorethan
ayearto10
years
Seasonalchanges(mostly
rainfall)
TheAknesrockslide
inNorway
may
generate
tsunam
isthat
killed
peoplebefore
35Oppikoferet
al.(2008)
Rock
TLS
60–70(upto
200)
1year
Rainfall,earthquakes,
miningoperations
and
snow
melt
TheAknesrockslide
inNorway
may
generate
tsunam
isthat
killed
peoplebefore
36Mihalinec
andOrtolan
(2008)
Clay
Comparison
oftopographic
maps
152–300
Over
33years
Rainfall
Urbancommunities
inZagreb,Croatia
37Lokin
etal.(1996)
Weathered
marlyclay
Inclinometers
102.5yearsand13
years
Toeerosion
SLOBOD
Abridge
inNoviSad,
Yugoslavia
38Bunza(2000)
Gravelandsilt
Extensom
eters
922years+4months
Rainfall,snow
meltand
erosion
Tiefenbach
village
near
Oberstdorf,
Germany
39Kalteziotis
etal.(1993)
–Inclinometers
13–19
Notindicated
–Thenationalroadfrom
Athens
toSounion
40Topaland
Akin(2008)
Interface
betweenclayey
layersandclaystone
Inclinometers
–Notindicated
Toeerosion
PipelinebetweenTurkey
and
Greece
41Fuchsbergerand
Mauerhofer(1996)
Shaley
graphite
Inclinometers
590
65days
Constructionactivities
Amotorway
intheAustrian
Alps
42Wanget
al.(2008)
Colluviu
mGPSandextensom
eters
180
3years
Rainfallandreservoir
levelfluctuations
Village
locatedon
theslope
oftheShuping
landslide,China
43Zhou
(2000)
Soilrock
interface
–2,000(a
maximum
ofmorethan
4,000)
53days
–SichuancityinChina
44Sunet
al.(2000)
Volcanicsaprolite
Airp
hotosandtopographic
maps
450
20years
Rainfall
Aroadsidecutslope
aboveLai
Ping
Road,Sha
Tin,China
45Wuet
al.(2008)
Coalbedswith
sandstones
andmudstones
Inclinometers
573years
Undergroundcoalmining
Hancheng
power
station,
China
46Baietal.(2008)
Finegrainedmaterial
–730
135days
Reservoirfilling
Lijiaxia
hydropow
erstation,
China
47Fujisaw
aet
al.(2007)
Earth
slide
Extensom
etersand
inclinometers
9,100
2months
Rainfall
Buildings
andwater
service
pipescollapsed
andapart
ofahighway
heaved
inJapan
48Maloneet
al.(2008)
Rock
Totalstationand
photogrammetric
surveys
7,000
3years
Rainfall
Newhighway
inMalaysia
49Kang
etal.(2000)
Incompetent
shales
–240
3yearsand9months
Bridge
construction
TheSugock
Bridge
inAndong,Korea
50Chandler
andBroise
(2000)
Sandysiltandclayeysilt
colluviu
mAirphotos
5,600
16years
Rainfall
Major
railw
aycorridorfrom
Colombo
toBodalla,Sri
Lanka
rupturesurface
measurementmethod
(mm/year)
monitoring
Technical Note
Landslides 8 & (2011)120
Canada, USA, Brazil, Ecuador, Australia, New Zealand, Italy,United Kingdom, Switzerland, Norway, Croatia, Yugoslavia,Germany, Greece, Austria, Turkey, China, Japan, Malaysia, Koreaand Sri Lanka. Some of the surveyed slides affect more than oneclass of facility, e.g., urban areas and highways or highways andother infrastructure. The reviewed cases are listed in Table 1. Eachgroup of slides occurring in the same country are groupedtogether. The order of countries is the same as mentioned earlierin this paragraph.
In addition to the rate of movement and the extent ofdamage, information regarding the method of displacement
measurement, the nature of the slide material and the maintrigger(s) of movement is presented. These attributes aresummarized in Table 1. The statistics presented are intended tobe helpful to geotechnical engineers dealing with slow-movingslides.
Displacement measurementThe methods used to measure the displacement play an importantrole in defining the mechanisms and the movement behaviour ofslow and extremely slow slides. A major issue when dealing with
Table 2 Advantages and disadvantages of different methods of measuring displacement
Instrumentation type Advantages Disadvantages
Manual inclinometers - Can measure displacements as low as a fractionof a millimeter.
- Slope indicator casings are broken at cumulativedisplacements of about 130 mm. Therefore, thelifetime is short in very slow and slow slides.
- Temporal resolution can be improved by increasingthe frequency of measurements, i.e., every day or less.
- Measure the displacement versus time at a single point.Thus, there is no spatial coverage for large sites. Hence,the technique is not economically feasible for large sites.
- Highly frequent monitoring of manual inclinometers isexpensive for remote sites in terms of a technician wages.
In-place Inclinometers - Overcome the temporal resolution drawback of manualinclinometers. The sensor is connected to a data-loggerthat records the displacements at intervals as shortas required.
- The location of the rupture surface should bedetermined before the installation of the in-placeinclinometers. Therefore, a slope indicator casingshould be installed first.
- Have the same drawback of the low spatial coverage asmanual inclinometers.
Extensometers - Measure the displacement by measuring the openingof cracks
- Do not measure large displacements and, hence, notsuitable for measuring displacements of slow slides or theupper range of very slow slides.
- Do not require deep installations - Measure the displacement at discrete points and, hence,do not provide good spatial coverage for large sites.
- Measure surface displacements rather than thedisplacement at the rupture surface elevation.
- Unable to determine the location of the rupture surface.
Remote techniques (InSAR, DInSAR,TLS, etc.)
- Suitable for measuring relatively large displacements (slowand the upper range of very slow movements), whichcannot be captured by inclinometers or extensometers.
- May not be able to capture extremely slow movementsover the monitoring interval, which is around a month.
- Overcome the spatial resolution drawback of the previoustechniques by providing coverage to large sites as long asreflective objects are present or installed at strategiclocations across the site.
- No coherence is expected to occur if no reflective surfacesexist or are installed.
- Measure the surface displacement rather than themovement of the rupture surface.
- Unable to determine the location of the rupture surface.
Surface surveying - Suitable for measuring relatively large displacements (slowand the upper range of very slow movements), whichcannot be captured by inclinometers or extensometers.
- Extremely slow movements may fall below the accuracyof the measuring instruments (total station).
- Overcome the spatial resolution drawback of inclinometersand extensometers by providing coverage to large sites aslong as surface targets are installed at strategic locationsacross the site.
- Measure the surface displacement rather than themovement of the rupture surface.
- The installation of surface targets for surveying is lessexpensive than installing corner reflectors for satelliteimagery.
- Unable to determine the location of the rupture surface.
Geomorphologic evidence - Very useful in quantifying long-term movements thatoccurred over many years and where there is no othermethod of measuring the movement.
- Cannot account for very slow or extremely slowmovements because of the small scale of air photos.
- Measure the surface displacement rather than themovement of the rupture surface.
- Unable to determine the location of the rupture surface.
Landslides 8 & (2011) 121
very slow or extremely slow slides is the low frequency of datarecording; hence, the trends of movement variation over timeoften are not clear. This hinders accurately determining therelative effects of different causal factors on movement. Inaddition, the movement rate is sometimes considered constant,while in fact it is not. Extremely and very slow movements consistof a viscous or creep component that is responsible for thepersistence of movement during periods without pore-pressurechange. The literature suggests that the slow movements ofshallow slides are affected mainly by changes in hydrologicalboundary conditions, while the viscous soil properties contributeto a large percentage of the movement of deep-seated slides(Picarelli and Russo 2004).
About 45 cases indicate the method of displacement measure-ment. Some of the surveyed slides were monitored using morethan one type of measurement. The methods used includedinclinometers, extensometers, remote techniques such as Syn-thetic Aperture Radar Interferometry (InSAR) and Terrestrial
Laser Scanning (TLS), surface surveying and geomorphologicevidence. A brief summary of the advantages and the drawbacksof each method is provided in Table 2. Inclinometers were used torecord movement in about 60% of the reported cases. However,because of the shearing-off of inclinometer casings when displace-ments reach around 130 mm, inclinometers were not used tomeasure the displacements of slides moving at rates of more than590 mm/year. In the upper range of very slow slides and in therange of slow slides, other methods, such as surface surveying,remote techniques, and geomorphologic evidence, become moreuseful to determine larger displacements over longer periods oftime. The lower precision of these methods may not allow them tobe used to accurately detect extremely slow movements. Remotetechniques such as InSAR and TLS were used in only 9% of thestudied slides. These techniques have been developed recently,and reliance on them should increase in the future as they providecoverage of large areas and overcome some of the disadvantagesof inclinometers. However, the increased application of in situ
Geomorphologic evidence, 13%
Remotetechniques, 9%
Surfacesurveying, 31%
Inclinometer, 58%
Extensometers, 9%
Fig. 1 Percentages of differentmethods of displacementmeasurement
Weak Rock, 27%
Rock, 10%
Soil, 53%
Interface, 12%Fig. 2 Percentages of differentmaterial types in the rupture surface
Technical Note
Landslides 8 & (2011)122
inclinometers can overcome the present issue of eventual loss ofaccess to the shearing zone. Figure 1 shows the percentages of useof each of inclinometers, surface surveying, remote techniques,extensometers and geomorphology in measuring the displace-ments of slow slides. The sum of the percentages of the differentmethods is more than 100% because more than one method ofdisplacement measurement was used in some of the surveyedcases.
Materials of the rupture surfaceOnly 48 of the studied cases explicitly state the type of thematerial in the rupture surface. More than half of these slides(52%) have rupture surfaces in soil materials, mainly clays and
silts. About 27% of the surveyed cases have rupture surfaces inweak rocks such as clay shales. The rupture surfaces run along theinterface between the soil and the underlying rock in 13% of thereviewed cases, and the rest have rupture surfaces in rockmaterials. The sum of the percentages is slightly higher than100% because one case (#4) involves more than one material typein the rupture surface.
Comparison across the cases suggests that the usuallyexpected hazards from rocky slopes are rock falls and topplingrather than sliding on a well-defined rupture surface. More thanhalf of the studied cases have their rupture surfaces in soil ratherthan rock. This observation, however, does not necessarilyindicate that sliding is the dominant mode of failure of earth
Mining activities,6%
Stream incision,23%
Rainfall, 64%
Anthropogenicactivities, 19%
Reservoir fillingand fluctuations,
11%
Earthquakes, 2%Snow melt, 4%
Fig. 3 Percentages of differenttriggers of movement
LinearInfrastructure, 9%
Dams, 11%
Railways, 5%
Highways, 23%
Urbansettlements, 40%
Bridges, 12%
Fig. 4 Percentages of citation ofdifferent vulnerable facilities in thereviewed literature
Landslides 8 & (2011) 123
Table 3 Summary of the case histories on the damage extent of urban communities due to slow-moving slides
Casenumber
Location Amount of damage Movement rate(mm/year)
Soil type Remarks
15 Italy No exact statement of damage butcould be minor
5 Quaternary deposits overlyingupper Miocene bedrock
16 Italy Cracks in buildings 8 – Cracks might be from buildingssubsidence
32 Switzerland Minor damage to village housesand infrastructure
10 Clay shales Development in the village is notaffected by slope movements
13 Australia Cracks in an embankment withinthe site in addition to somebent trees
12 Colluvium over residual soilsoverlying bedrock
25 UnitedKingdom
It is considered that there could be athreat to a coastal road in a town
12 Well jointed rock with noshear surfaces
1 Peace Rivertown,Canada
Removal of a portion of a streetand structural distress to somehouses
14 Glacial deposits overlyingpreglacial lake clays overclay shale
17 Italy Open cracks, wall disjunction andbadly working casings
16.2 Authors classified this damage as lightto moderate
18 Italy Damage to dwelling houses 26 Marly clay
34 Norway Minor damages could occur toresidential settlements and towns
30–100 Rock A wide-scale study.
A warning system was designed wherethe recorded rate lies in the greenrange (safe and no damagesexpected)
11 Brazil Cracked pavements in streets anddamages to houses
80 Interface between colluviumand clayey siltstone
26 UnitedKingdom
Cracks in roads and footpaths of atown and damage to seawallstructures
91 –
38 Germany The slides threatens a village bydebris flow
92 Gravel and silt
2 Reginabeach,Canada
Rupture of service utilities, groundcracking. No damage toconcrete sidewalk
108 Bentonitic clay shales The study concluded that 100 mm/yearis enough to break a municipalwater line
42 China Cracks in roads and houses of aresidential settlement on aslope
170–240 – The toe is the Three Gorges Damreservoir but the study is about thedamage to the residential settlementson the slope
36 Croatia Houses suffered damage (notspecified)
150–300 Clay
35 Norway Minor to moderate damage mayoccur to residential settlements
200–365 Rock
9 USA Cracks in houses 306 Plastic lacustrine clay
Walls buckling
Bending of doors and windows
Damage of the rear wall of a garageby downslope movement
27 UnitedKingdom
Movement led to major slopefailures below a hotel building
861 Stiff, fissured overconsolidatedBarton clay
43 China Cracks in a slope within aresidential complex
2000(a maximumof more than4,000)
Soil rock interface Because of the implementation of awarning system, the buildings wereevacuated and no life losses tookplaceSevere damage to the backwall of
a building
19 Italy Severe damage to Crago villagebuildings
4,000 –
12 Ecuador Parts of some houses of the city ofLoja were separated by 1 m in2 months
6000 –
47 Japan Collapse of a car repair factory 9,100 –
Technical Note
Landslides 8 & (2011)124
slopes. Figure 2 shows the percentages of slides having theirrupture surfaces in soil, rock and weak rock and at the interfacebetween soils and rocks.
Trigger(s) of movementSome of the cases have more than one identified movementtrigger, although the majority have a single identified trigger.
Forty-seven cases report the trigger(s) of the slow movement ofslides. Rainfall is the main trigger in 64% of the reviewed slides.This finding suggests that designing and installing drainagemeasures are important for facilities constructed in heavy-rainfallareas. Toe erosion and human activities are the triggers (or one ofthe triggers) of movement in about 42% of the surveyed slides.Reservoir filling and seasonal fluctuations in reservoir levels seem
Table 4 Summary of the case histories on the damage extent of highways and railways due to slow-moving slides
Casenumber
Location Amount of damage Movement rate(mm/year)
Soil type Remarks
28 United Kingdom Cracks in road pavement 13.8 Glacial deposits overlyingboulder clay
Road needed re-pavementevery 3 or 4 years
39 Greece Cracks in the pavement of amajor highway
13–19 –
18 Italy Traffic disruption to a highway 26 Marly clay
3 Alberta, Canada Cracks in a highway thatneeded patching once ortwice a year
35 Presheared bentonitic clayshale over sandstone
20 Italy Damage not specified 44 Softened clay A previous reactivation caused lotsof damage and has interrupted amajor road and highway
4 Alberta, Canada Cracks in highway 49 Minimum of 15and up to 100
Till overlying preglacial lakeclay and clay shale
Patching performed once ayear
21 Italy Damage not specified but notsevere
65 Quaternary deposits inaddition to dislocatedbedrock
A previous reactivation led to thecollapse of a long stretch of anational road
22 Italy Undefined threat to a road anda railway
132 Intensely fissured clay shaleand limestone over abedrock
44 China No quantification of damagereported
450 Volcanic saprolite overcompetent bedrock
Severe rainstorm events cause roadblocking
29 United Kingdom No damage reported to acoastal road
560 Sedimentary rocks overlainby glacial till
This rate was recorded afterremedial measures havebeen installed
41 Austria Development of large fissuresand failures in the cut slopesof a motorway
590 Intensely sheared shaleygraphite layer
A major traffic disruptionexpected if no drainagemeasures were adopted
30 United kingdom Traffic obstruction of a trunkroad
600–6000 Glacial till overlying asequence of mudstonesand siltstones
Breach of the boundarybetween the road and therear garden of a residentialproperty
50 Sri Lanka Severe disruption to a railwaycorridor
5,600 Sandy silt and clayey siltcolluvium
48 Malaysia Disruption to a highwayconstruction
7,000 Rock (schist)
47 Japan Upheaval of a part of ahighway
9,100 –
Landslides 8 & (2011) 125
Table 5 Summary of the case histories on the damage extent of bridges due to slow-moving slides
Case number Location Amount of damage Movement rate(mm/year)
Soil type Remarks
37 Yugoslavia No actual damage to the SLOBODA bridge,but there is a threat.
10 Weathered marly clay
Mitigation plans are set for probabledistress in the future
31 United Kingdom Continuous movement of abutment and piers 23 –
33 Switzerland Numerous cracks in the abutment of a bridgecaused by a very high flood
60 –
5 British Columbia,Canada
Displacement of one of the Peace River suspensionbridge anchors led to the bridge collapse
90–120 Clay shale
4 Alberta, Canada The Little Smoky bridge south pier needscontinuous extension to accommodatemovements
100 Till overlying clay shale
10 USA The Bismarck bridge pier needs continuousextension to accommodate movements
100 Clay shale
49 Korea Bridge suffered severe deformations 240 Alternating competentsandstones and incompetentshales
Table 6 Summary of the case histories on the damage extent of dams due to slow-moving slides
Casenumber
Location Amount of damage Movement rate(mm/year)
Soil type Remarks
6 British Columbia,Canada
Minor or no damage to Mica Dam 10–14 Rock slide moving on thin claygouges
45 China Serious damage to the Hancheng powerstation structures
57 –
24 Italy Fissures and cracks observed in Casanuovadam
110 Softened clay layer
23 Italy Damage to the electric cabin and theguardian’s house of Trinita Dam
127 Highly permeable formation overa weathered clay formation
No damages to the dam
14 New Zealand Slide volume is enough to block the Clydedam reservoir
180 Planar rock slide moving overslickensided sandy silt claygouge
The slide-generated waves are expectedto be higher than the free board
46 China Failure of localized disintegrated looseslide mass on the surface of the slope
730 Fine-grained material with a claypercentage sometimes morethan 90%
Slide-generated waves may endanger thehydropower station
Table 7 Summary of the case histories on the damage extent of linear infrastructure due to slow-moving slides
Case number Location Amount of damage Movement rate (mm/year) Soil type Remarks
7 Alberta, Canada Bending of oil well casing(Swan Hills Oil Field)
100 –
5 British Columbia,Canada
Break down of a pipeline 90–120 Clay shale
8 Fort McMurray, AB,Canada
Displacement of pipelines 188 Glacial deposits overlying Cretaceoussedimentary clay shale over oil sands
47 Japan Rupture to a water service pipe 9,100
Technical Note
Landslides 8 & (2011)126
to affect slopes that lie upstream of dams, as these factors triggerthe movement of about 11% of the studied cases. Other triggerssuch as earthquakes, snowmelt and mining activities are respon-sible together for the sliding in about 12% of the reviewed cases.Figure 3 shows the percentages of the contribution of differenttriggers to slow-slide movements.
Classes of vulnerable facilitiesThe vulnerable facilities include the five categories mentionedabove: urban and suburban settlements, highways and railways,bridges, dams and linear infrastructure. In 40% of the reviewedcases, the vulnerable facilities are urban and suburban commun-ities. This high proportion is expected due to the direct threatposed to human life when towns are built close to natural moving
slopes. The vulnerabilities of highways and railways are docu-mented in 23% and 5% of the studied cases, respectively. Highwayand railway hazards can be life-threatening to travellers. The levelof threat is, however, less than that to urban communities.Figure 4 shows the relative citations of the different types ofvulnerable facilities among the studied cases.
Damage extentTwenty-two of the reviewed cases described the extent of damageto urban and suburban communities. The cases are sorted inascending order of the slide velocities, starting from a measuredrate of 5 mm/year up to 9 m/year. The case numbers in Table 3 arelinked to Table 1. Table 3 presents a summary of these cases,focusing on the extent of damage resulting from slides with
Strain
Time(a) (b)
Prim
aryLog (Time)
Log (Strain Rate)
Secondary
Ter
tiary
Primary
Secondary
Tertia
ry
Fig. 5 Primary, secondary and tertiary creep stages from a typical triaxial test shown on both: (a) arithmetic and (b) logarithmic scales (Modified after Augustesen et al.2004)
Table 8 Damage expected from slow-moving slides to urban communities versusmovement rate
Movement rate(mm/year)
Extent of Damage
0–10 - Minor or no damage
10–100 - Cracks in streets, footpaths and nearby embankments
- General signs of distress like bent trees
- House walls disjunction and badly working casings
- May cause damage to small dwelling houses
100–300 - Cracks are wide to the extent that houses start to suffera noticeable damage
- Rupture of service utilities
300–800 - House walls buckling, bending of doors and windowsand various damages in houses
800–4,000 - Severe damage and failures to slopes or retainingwalls supporting buildings
- If no warning system is implemented, human lossesmay occur
>4,000 - Complete collapse of buildings
Table 9 Damage expected from slow-moving slides to highways versus move-ment rate
Movement rate(mm/year)
Extent of damage
0–10 - Minor or no damage
10–100 - Cracks start to appear
- Developed cracks need patching once or may be twicea year
- Needs re-pavement once every 3 or 4 years
- May cause traffic disruption
100–160 - Wider cracks in pavements
- Need patching at intervals less than 1 year
160–1600 - Development of large fissures in embankment slopes
- Failure may occur to embankment slopes
- A major traffic disruption is expected if no drainagemeasures were implemented
>1600 - Severe collapse to the highway or the railway
- Traffic obstruction
- May lead to life losses
Landslides 8 & (2011) 127
different velocities. All of the cases are compiled to qualitativelyrelate the expected damage to urban communities resulting fromslow-moving slides. The relationship describes the expectedincrease in damage to urban communities from increasing slidevelocities (or slide displacements) within the ranges of slow, veryslow and extremely slow slides. The qualitative relationship ispresented in Table 8 and graphically in Fig. 6.
Tables 4, 5, 6, 7 similarly summarize the extent of damageresulting from slides moving at different rates that adversely affecthighways and railways, bridges, dams and linear infrastructure,respectively. Table 4 indicates that only cases 22 and 50 documentdamage to railways. Hence, it is considered that the availableinformation about the vulnerability of railways to slow-movingslides is not enough to develop a general description of the expecteddegree of damage to railways. Therefore, Tables 9, 10, 11 show thequalitative expected extents of damage from different slide velocitiesfor highways, bridges and dams, respectively. Unlike the casesdescribing urban-community damage, the cases summarized inTables 9, 10, 11 do not reveal a wide spectrum ofmovement rates. Thedamage extents for highways, bridges and dams show that theexpected extents of damage occur at different limits of movement.
Pipelines and water-reticulation pipes are examples of linearinfrastructure. Only four cases are available with sufficient data, asshown in Table 7. A fifth one has a qualitative description of the threatposed by a slow-moving earth slide to a pipeline. The limited numberof available cases makes it difficult to relate the extent of damage topipelines and water service pipes by the movement of slow-movingslides.
DiscussionThe study presents simple statistics about the different attributesof slow-moving slides. In addition, it relates qualitative damageextents or damage descriptions to annual movement rate (or total
Table 10 Damage expected from slow-moving slides to bridges versus movementrate
Movement rate(mm/year)
Extent of damage
0-10 - Minor or no damage
10–30 - Movement of piers and abutments take placebut cracks may be very small
- Mitigation plans should be set for probablefuture distress
30–100 - Numerous cracks start to appear
- There is a continuous need to extend the bridgepiers and abutments to accommodatemovements
>100 - Deformations become severe and pose a realthreat to the bridge safety
- Suspension bridges may collapse if the bridgeanchors lied in the movement zone
Table 11 Damage expected from slow-moving slides to dams versus movementrates
Movement rate(mm/year)
Extent of Damage
0–16 - No reported damage
16–160 - Serious damage to hydropower structures
- Fissures and cracks may be observed in earth androck fill dams
>160 - Failure of loose masses on the slope surface andhence the reservoir may be blocked
- Slide-generated waves may overtop the dam crest
1 10 100 1,000 10,000 100,000 1,000,000
160
m/y
r
Minor
Moderate
Major
Severe
Urban Communities
Highways
Bridges
Dams
Urban Communities
Highways
Bridges
Dams
Urban Communities
Highways
Bridges
Dams
Urban Communities
Highways
Bridges
Dams
Movement Rate (mm/yr)
Deg
ree
of D
amag
e
Fig. 6 Schematic representation of the expected extent of damage versus movement rate for various forms of infrastructure. Green color indicates minor damage,orange indicates moderate damage, yellow indicates major damage, and red indicates severe damage
Technical Note
Landslides 8 & (2011)128
displacement). It should be noted, however, that the damagedescriptions corresponding to every movement-rate range isbased only on the shown range. The extent of damage willbecome more severe if proper mitigation measures are notapplied promptly to prevent the movement accumulating. Forexample, minor or no damage would result from a movement rateof 5 mm/year if the proper mitigation strategies are applied in atimely manner. However, if there has been no attempt to arrestthe movement for 10 years, for example, the cumulative move-ment may become around 50 mm. This movement magnitude willbring the resulting damage to a higher level, which may bedestructive in some cases. Therefore, it is the cumulativedisplacement that ultimately controls the extent of damage ratherthan the annual movement rate.
Another problem is associated with extremely slow move-ments. Extremely slow slides are often considered as moving at aconstant rate, unless a comprehensive program of monitoring thedisplacement over very short intervals is implemented. While thisconstant-rate movement is considered a creep displacement, thestrain–time curve in a creep test in a triaxial apparatus shows thatthe strain rate decreases, remains constant and then increasesuntil failure during the primary, secondary and tertiary creepstages, as shown in Fig. 5. The laboratory creep behaviour impliesthat creeping landslides may change to be extremely rapid afterlong periods of observed decreasing movement rate. Theevolution of catastrophic movements from creep displacementsis a quite complex mechanism. Petley and Allison (1997)mentioned some basic patterns that control the relationshipbetween creep and catastrophic movements. Creep may continuefor long periods of time during which the displacement rate isessentially constant, but may show minor fluctuations due tosmall changes in the water table. Another pattern is incrementalcreep, in which pore pressure changes and/or seismic events maycause changes in the rate of displacement. Deep-seated slides maysimilarly undergo short periods of creep followed by suddenfailure. Finally, a deep-seated slide may undergo long-term creepdisplacements followed by a sudden failure.
Schuster and Highland (2007) have pointed out the adverseeffects of landslides on the natural environment in general. Theirstudy discussed the vulnerability of each of the mountain andvalley systems, i.e., the earth’s surface morphology, the rivers andstreams in terms of water quality, forests and grasslands, and thenative wildlife to landslides. Our study investigates a specificaspect of the issue by highlighting the vulnerability of differentkinds of facilities to a particular type of landslides—slow-movingslides. Based on the outcomes of this study, we agree with theconclusions of Schuster and Highland (2007) that typical risk-management strategies, including (1) restricting development inlandslide-prone areas, (2) implementing building codes, (3)design of physical mitigation works and (4) developing andinstalling landslide-monitoring and warning systems, could beadopted to reduce the impacts from these types of landslides.
ConclusionsThe paper has reviewed about 50 cases relating to the vulner-ability of different kinds of facilities to extremely slow, very slowand slow-moving slides. The results indicate the types oflandslides and their associated ranges in movement rates; whattypes of equipment are routinely used to monitor these types of
landslide; the movement triggers; and the impacts. This literaturesurvey allowed us to relate qualitative expected extent of damageto movement rate for urban communities, highways, bridges anddams threatened by extremely slow, very slow and slow-movingslides. The extent of damage to each of the studied facilities iscategorized into minor, moderate, major and severe. Thetabulated relationships shown in Tables 8, 9, 10, 11 are shownschematically in Fig. 6, which reveals that buildings andresidential houses may tolerate higher slide velocities and totaldisplacements than the other facilities before experiencing seriousdamage. Bridges are the least tolerant facilities, for movementrates as low as 100 mm/year may severely damage bridges withina year, whereas such low rates may cause only moderate damageto urban communities.
Slow landslides can, however, become rapid landslides ifconditions change. For creeping landslides, however, it is usuallythe cumulative total displacements that cause problems toinfrastructure and housing.
The study has an important practical significance for geo-technical engineers as it provides a way of assessing the likelyextent of damage based on preliminary estimates of movementrates. Hence, the proper field investigation program can beplanned, and the appropriate remedial measures can be imple-mented. In addition, alarm systems can be designed based on themeasured movement rates in the field.
AcknowledgmentsThe authors would like to thank the Natural Science andEngineering Research Council of Canada for providing thefinancial support of the project.
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